1. Field of the Invention
This invention relates to a filter package containing a filter immersed in a liquid and to a method of forming such a filter package. More particularly, it relates to a filter package the contents of which are sanitized and preferably sterilized.
2. Description of the Related Art
It is common for filters to be stored and shipped in a wet state, immersed in a suitable liquid within a package. There are several reasons for packaging a filter in this manner. Some filters are not readily wettable by the liquid which they are intended to filter and so are usually prewetted with another liquid having a lower surface tension to prepare the filter for filtration. As a service to the customer, some filter manufacturers perform prewetting at the factory where the filter is manufactured. In order to prevent the prewetted filter from drying out during storage or shipment, the filter is packaged in a sealed bag containing a suitable liquid which keeps the filter wetted until it is ready to be used.
Other types of filters, such as ultrafiltration and reverse osmosis membranes, are not xe2x80x9cprewettedxe2x80x9d by the manufacturer but are nevertheless shipped to the customer in a wet state in order to maintain their permselective properties. These filters are typically stored and shipped in packages containing a humectant such as glycerin which keeps the filter wet.
Another reason for packaging a filter in a wet state is that it is easier to ensure the cleanliness of such a filter than if it is packaged in a dry state. Thus, even filters which do not require prewetting and which do not need to be kept wet to maintain their filtering properties may be packaged in a wet state for reasons of cleanliness.
In order to give a filter package containing a wet filter a suitable shelf-life, hydrogen peroxide or other bactericide is usually added to the liquid within the package in order to prevent bacterial growth between the time of manufacture and the time that the purchaser opens the package.
Even though the amount of the bactericide is relatively small (typically around 3% in the case of hydrogen peroxide), in some applications, and particularly in the manufacture of semiconductors, the bactericide is an undesirable contaminant. Accordingly, there is a need for a filter package containing a filter in a wet state which has a long shelf-life yet which contains substantially no contaminants.
In accordance with one aspect of the invention, a filter package having a long shelf-life and containing substantially no contaminants comprises a filter cartridge, a flexible bag surrounding the filter cartridge having walls comprising a polymeric material impervious to microorganisms and liquid water, a venting mechanism formed in a wall of the flexible bag, and sanitized water sealed inside the flexible bag and immersing substantially 100% of a volume of the filter cartridge. The filter cartridge includes a porous filter medium having a plurality of pores through which a fluid can pass between an upstream side and a downstream side of the filter cartridge and the sanitized water substantially permeates the pores of the filter medium. The venting mechanism includes a vent filter preventing the passage of microorganisms into the flexible bag.
The contents of the filter package of the present invention are at least sanitized, i.e., all or substantially all non-spore producing microorganisms are killed, and preferably the contents of the package are fully sterilized. In this description, xe2x80x9csterilizingxe2x80x9d is included within the scope of the term xe2x80x9csanitizingxe2x80x9d. Thus, a sanitized filter package according to the present invention may be one which has been fully sterilized or one which has been sanitized without being fully sterilized.
The sanitizing can be performed in any manner which will not damage or degrade the filter or the container. In preferred embodiments, sanitizing is performed by heating the liquid and the filter within the container. When sanitizing is performed by heating, the container may be vented during sanitizing to permit vapor of the liquid to exit from the container and prevent the build-up of pressures which could damage the container.
A filter package according to the present invention is not restricted to one having any particular type of filter. For example, the filter may be either hydrophilic or hydrophobic, it may be a filter for filtration of gases, liquids, slurries, or mixtures of more than one phase, and the mechanism by which it performs filtration is not important. A few examples of various types of filters which may be employed in the present invention are particulate filters, particularly for use in the semiconductor industry, coalescers, ultrafiltration membranes, and reverse osmosis membranes.
If desired, the filter may be prewetted prior to being immersed in liquid in the container so that it can be completely wetted by the liquid in which it is immersed.